This invention relates to anti-skid devices, useful for example in snow or mud conditions, and in particular a type of device which can be mounted directly on a motor vehicle's wheel having a rim and tire. The anti-skid device is designed as a yoke or stirrup which embraces the tire and claws are provided at the yoke ends in order to engage with the shoulder of the rim.
Devices of this kind are intended to serve as an alternative to snow chains and are especially useful in instances where a vehicle is stuck in a rut, such as in snow, and cannot move. In such a case, tire chains could at best, be installed only under considerable difficulties whereas the present invention in the form of individual yokes or stirrups can be fitted comparatively simply at accessible positions around the tire. If, after fitting one or two such anti-skid yokes or stirrups, the relevant wheel still slips or falls to grip, the wheel can be stopped at new positions so that further anti-skid yokes or stirrups can be fitted to the tire.
In one known device in which a U-shaped yoke or stirrup engages the associated rim shoulders by claws, the yoke or stirrup consists of a non-bendable iron metal. One yoke or stirrup limb is hinged so that it can be swung out and is lockable by means of a leaf spring in its closure position. The angular position of the yoke limbs is adjustable relative to the central part of the yoke by means of screws. The fastening principle involved in this yoke makes use of the fact that the central part of the yoke is forced away from the rim periphery by tire pressure and in this way the claws are drawn under the rim shoulders.
Therefore the yoke must, when it is fitted, be pressed as firmly as possible by its central part onto the pneumatic tire, so that after swinging in of the yoke limbs, engagement of the claws under the rim shoulders, and release of the pressing force, it is firmly retained by this tire pressure. Naturally this mounting procedure requires considerable and strenuous effort.
Moreover when the yoke is in the lowermost position at the bottom of the wheel, the wheel load acts in opposition to the tire pressure. Accordingly, because of the rigid design of the yoke, the claws can become disengaged from the rim shoulder, and the yoke can, under propulsive force applied through it, tilt in the circumferential direction of the wheel. This represents a considerable danger of damage to the tire, it being possible for the central part of the yoke to be forced by its side edge into the thread of the tire. Moreover, the tire is confined by the rigid yoke, so that it cannot deform in the manner intended from its design.
In contrast the preferred embodiment of this present invention provides a simple and rapidly-mountable anti-skid device which seats securely on the tire even under load conditions.
In accordance with the invention, this is achieved by providing, in the case of an anti-skid device of the kind referred to in the introduction to this specification, for the claws at the yoke or stirrup ends to be equipped with adhesive magnets.
The magnets attached to the claws assures that the claws will not become disengaged from the rim's shoulder even when the yoke limbs transmit wheel loads to the claws which endeavor to lift the claws off from, or draw them away from the shoulder surface on which they are seated.
In appropriate circumstances, the yoke limbs, as well as the yoke web, may be rigid in design in which case one and/or both yoke limbs may be hinged to the yoke web. However, in the present invention it is preferred to make the yoke limbs pressure-yielding, so that forces acting on the yoke web cannot be transmitted to the claws and counteract the positioning thereof as held by the magnets.
By employing resilient yoke limbs the risk of damage to the tire can be avoided since compressive forces will not be transmitted in the longitudinal direction of the yoke limbs from the yoke web to the claws. Thus, the yoke may be made, at least in the region of its limbs, from an elastically pliable strip material, preferably preshaped to correspond with the outer cross-sectional contour of the tire. By fabricating the yoke limbs from an elastically pliable material it allows the yoke to adapt to deformations of the pneumatic tire, so that the tire is not pinched or squeezed, although the yoke is seated securely on the tire under all loads, by the magnets on the claws. In this respect, the magnets in or on the claws ensure that the claws remain in position on the shoulder surface of the rim and do not slip off from or become disengaged from the shoulder even when the yoke limbs are anchored outwards as a result of loading of the yoke under the wheel load, and creates, on the claws, a pull component which extends parallel to the shoulder surface and under the effect of which the claws might otherwise slip or be moved off the shoulder face.
Further, by employing magnets with the claws the yoke or stirrup can also be effectively used when the relevant shoulder surface of the rim extends slightly obliquely.
By thickening the yoke in the region of its longitudinal center which is positioned on the tread of the tire, a comparatively thin strip material can be used for the rest of the yoke and still provide a sufficient projecting thickness above the tire tread to obtain effective anti-skid protection.
The claws on the anti-skid yoke of the device of the invention can be designed to suitably engage with either the rim shoulders or under the rim flange.
Although the strip material of the yoke may, for example, be comprised of a plastic or rubber material which is sufficiently elastic at low temperatures, it is preferred to make the yoke from a bendable material, preferably a spring-steel strip, which is coated, at least in the longitudinal center of the yoke, with an elastic covering or jacketing. When the yoke is made from bent strip material, in appropriate circumstances the adhesive action of the magnets may be smaller, so that no magnets, or only weak magnets, may be sufficient if the distance of the claws from one another, when the yoke is not fitted is smaller than in the case where the yoke is fitted to the tire. In this case the yoke is opened by resiliently bending its limbs away from each other for fitting to the tire and, therefore, when fitted, acts like a spring clip under the bias of which the claws are pressed axially toward one another and toward the rim.
By covering or jacketing the strip material forming the yoke, the thickened yoke region is formed at the yoke web. Preferably the covering or jacketing also extends as far as the underside of the yoke, so that the ability of the yoke to adhere to the tire profile is improved. In order to achieve good anchorage of the covering or jacketing on the spring steel strip a plurality of holes may be provided in the strip material which will be penetrated by the elastic covering or jacketing.
While the thickened region of the yoke may be formed with a smooth outer surface the gripping capacity is increased if the thickened region of the yoke is equipped with coarse profile, such as by including studs which correspond to the sort of stud profile used on snow tires.
So as to obtain good support of the anti-skid yoke against possible lateral tilting which could occur as a result of propulsive forces acting laterally thereon, the claws on the yoke limbs should be as wide as possible. If the strip material is not wide enough for this purpose, the claws can be designed as T-shaped members so that support arms extend outwardly beyond both side edges of the yoke.
in a further development of the device the anti-skid yoke can be adapted to different tire profiles by having the length of the yoke be variable or adjustable. Suitable adjusting means for adjusting the length of at least one limb of the yoke limbs could be comprised of an adjustable screw device connected to at least one of the yoke limbs. This can, for example, be achieved by dividing the relevant yoke limb into two parts and by riveting or welding a screw to the end of one part with this screw extending through a slotted hole formed in the other part of the yoke limb and then using a wing nut to hold the two parts together and which would allow the length of that limb to be variable. However, it is also possible to provide a screw adjusting device similar in its operation to those used on hose clamps in which the screw axis extends parallel to the strip material, so that by rotating the screw the yoke parts can be drawn together, or pushed apart, in the longitudinal direction of the yoke. When the strip material forming the yoke is made from spring steel strip, in which the yoke limbs in their relaxed conditions have an outwardly arched configuration, it is generally sufficient to adjust the yoke length to adapt it to the associated tire only once, because by manually indenting or deflecting the bent yoke limb inwards the distance of the claw from the center part of the yoke is enlarged, so that when fitting the claw on the wheel, the claw can be easily pushed under the shoulder surface of the rim, against which it is closely applied after the yoke limb has been released.
This permits simple fitting of the anti-skid yoke of the invention, even when the length of the yoke is not adjustable.
For further simplification of the fitting operation, at least one of the yoke limbs may be constructed so as to be resilient in its longitudinal direction, for example it may be made, as a whole, from a resiliently extensible rubber or plastic material. When at least one of the yoke limbs is resilient in its longitudinal direction, in addition to simplifying fitting, one obtains the further advantage that the claws of the yoke are pressed against the associated shoulder surface of the rim when the central region of the yoke is displaced, under wheel loads, radially towards the edge of the rim. Instead of making the entire yoke limb so as to be longitudinally resilient, a spring body, for example a rubber strip or a spiral spring, can be incorporated in the limb.
A suitable material for the covering of jacketing of the anti-skid yoke of the invention is, for example, an abrasion-proof polyamide/polyester/butadiene compound having a cold resistant softener which keeps embrittlement of the material, which occurs at low temperatures, within acceptable limits. A small ceramics magnet of high performance may be used as the magnet for the claws.
In a currently-preferred embodiment of the invention, there is a special arrangement of the magnets in the yoke claws to achieve a particularly strong adhesive effect for the yoke claws on the wheel rim. The claws can, for example, be comprised of two plates made of magnetizable material, which are spaced from one another and between which the magnets are arranged with their poles lying on the plates, on the plate plane extending parallel to the plane of the yoke.
With this design of the claws, a magnet substantially of horseshoe configuration is achieved, where the magnet limbs are formed by the plates of the claws, so that, upon fitting the plates with their inner front edges against the shoulder surfaces of the rim, a considerable strengthening of the magnetic attractive force is achieved as compared with the case where the magnets are placed only with one magnet pole against the shoulder surface of the rim.
In the preferred embodiment of an anti-skid device made according to the present invention, the inner front edges of the plates are formed so as to be complementarily to the contour of the rim shoulder surface on which they are intended to act. This assures the contact surface over which the inner front edges of the plates butt against the rim and on which the magnetic attractive force acts will be as large as possible. Further, the inner edges of the plates could be provided with recesses which approximate the angle-shape configuration of the shoulders of the rim.
The magnetic attractive force between the claws and the wheel rim can be additionally improved if, instead of using a single magnet, several magnets are provided, these being arranged side-by-side between the plates of each claw.
Although also the yoke can be made from an elastically bendable strip material which is thickened in the region of the longitudinal center of the yoke, the yoke web which rests on the tread of the tire may be rigid in design, and made, for example, from an iron material. Preferably the yoke limbs are formed by helical springs which connect on the one hand with the yoke web and on the other hand with the claws. For this purpose, the plates can be connected together via a web or crosspiece in which the helical spring which connects the claws to the yoke web is suspended.
Instead of a design made from helical springs, the yoke limbs may be from an elastically bendable strip material or a deformable strip material. In this case, as in the case of the above-described first embodiment, adjusting means for the length adjustment of at least one of the yoke limbs, may be present.